Electric Machine with Q-Offset Grooved Interior-Magnet Rotor and Vehicle

ABSTRACT

A rotating electric machine includes a stator having a stator coil and a rotor provided rotatably around a specific rotation axis with respect to the stator. The rotor includes a plurality of magnets, a plurality of magnetically-assisted salient pole members provided between poles of any adjacent two magnets from among the plurality of magnets, and a magnetoresistance variation unit provided in the magnetically-assisted salient pole member along an axial direction of the rotation axis at a position offset in a circumferential direction of the rotation axis from a q-axis passing through a salient pole center of the magnetically-assisted salient pole member. The amount of offset of the magnetoresistance variation unit from the q-axis varies depending on positions of the magnetically-assisted salient pole members so that torque fluctuations cancel each other when power is applied.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/046,813, filed Feb. 18, 2016, which is a continuation of U.S.application Ser. No. 13/124,502, filed Apr. 15, 2011, issued on Mar. 29,2016 as U.S. Pat. No. 9,300,176, which is a National Stage of PCTInternational Application No. PCT/JP2009/067795, filed Oct. 14, 2009,which claims priority from Japanese Patent Application No. 2008-266952,filed on Oct. 16, 2008, the disclosures of which are expresslyincorporated by reference herein.

TECHNICAL FIELD

The present invention relates to a rotating electric machine and anelectric vehicle equipped with the rotating electric machine.

BACKGROUND ART

Motors for driving used in electric vehicles and hybrid vehicles arerequired to provide significant power output so that permanent magnetmotors including a rare earth element that retains intense energy aregenerally used. The motors for driving use, from among such permanentmagnet motors, embedded-type magnet motors, which can satisfy therequirement to provide a large torque at low speeds and a wide rotationspeed range.

Torque fluctuations of a motor are causes of noises and vibrations. Inparticular, in the case of electric vehicles, there arises the problemthat the torque fluctuations make the ride uncomfortable at low speeds.Conventional motors generally adopt a countermeasure to provide skew inorder to reduce the torque fluctuations. For example, there is known amotor in which an electromagnetic steel sheet provided with grooves isarranged on the side of outer periphery of a magnet embedded in a rotorand the grooves are arranged as being displaced in a direction along theperiphery of the rotary shaft one portion from another.

CITATION LIST Patent Literature

[Patent Literature 1] JP 2005-176424 A

SUMMARY OF INVENTION Technical Problem

In the case of the motor described above that is provided with grooveson the side of outer periphery of the magnet, the grooves are arrangedat positions where magnetic fluxes flow in each of cases when power isapplied and when power is not applied. As a result, a problem arises.For example, if the grooves are provided at positions such thatfluctuations when power is on are decreased, cogging torque isincreased, and on the other hand, if the grooves are provided atpositions such that the cogging torque is reduced, the torquefluctuations when power is applied are increased.

An object of the present invention is to improve the performance (forexample, efficiency, reliability, cost performance, or productivity) ofa motor.

Solution to Problem

A rotating electric machine according to a first aspect of the presentinvention includes a stator having a stator coil and a rotor providedrotatably around a specific rotation axis with respect to the stator.The rotor includes a plurality of magnets, a plurality ofmagnetically-assisted salient pole members provided between poles of anyadjacent two magnets from among the plurality of magnets, and amagnetoresistance variation unit provided in the magnetically-assistedsalient pole member along an axial direction of the rotation axis at aposition offset in a circumferential direction of the rotation axis froma q-axis passing through a salient pole center of themagnetically-assisted salient pole member. The amount of offset of themagnetoresistance variation unit from the q-axis varies depending onpositions of the magnetically-assisted salient pole members so thattorque fluctuations cancel each other when power is applied.

According to a second aspect of the present invention, it is preferredin the rotating electric machine according to the first aspect that themagnetoresistance variation unit is a magnetic air gap.

According to a third aspect of the present invention, it is preferred inthe rotating electric machine according to the second aspect that thecircumferential positions of the magnets in the rotor are constantregardless of the positions in the axial direction.

According to a fourth aspect of the present invention, in the rotatingelectric machine according to the second aspect, the rotor may bedivided into a plurality of axial-direction split cores that areprovided along the axial direction and each of which has the magnet, themagnetically-assisted salient pole member, and the magnetic air gap. Itis preferred that the circumferential positions of the magnets in theaxial-direction split cores are constant regardless of the positions inthe axial direction.

According to a fifth aspect of the present invention, in the rotatingelectric machine according to the fourth aspect, the rotor may include aplurality of core groups each consisting of a plurality of theaxial-direction split cores that have substantially the same positionsof the magnetic air gaps in the circumferential direction. It ispreferred that a sum of thicknesses of the plurality of axial-directionsplit cores constituting the core group in the axial direction isconstant for each of the plurality of core groups.

According to a sixth aspect of the present invention, in the rotatingelectric machine according to the second aspect, the magnetic air gapmay be a concave formed on a surface of the rotor.

According to a seventh aspect of the present invention, it is preferredin the rotating electric machine according to the sixth aspect that theconcave has a width angle in the circumferential direction that iswithin the range of ¼ to ½ times a pitch angle between any adjacent twoof teeth provided in the stator.

According to an eighth aspect of the present invention, in the rotatingelectric machine according to the second aspect, the magnetic air gapmay be a hole formed on a surface of the rotor.

According to a ninth aspect of the present invention, it is preferred inthe rotating electric machine according to the eighth aspect that thehole is formed integratedly with a hole in which the magnet is provided.

According to a tenth aspect of the present invention, it is preferred inthe rotating electric machine according to the first aspect that theplurality of magnets is arranged in the circumferential direction suchthat a direction of magnetization of each magnet is in a radialdirection of the rotor that is perpendicular to the axial direction andan orientation of magnetization of each magnet is alternately reversed.

According to an eleventh aspect of the present invention, in therotating electric machine according to the tenth aspect, each of themagnets may constitute a magnet group consisting of a plurality ofmagnets having substantially the same orientation of magnetization.

According to a twelfth aspect of the present invention, in the rotatingelectric machine according to the second aspect, themagnetically-assisted salient pole member may be provided with aplurality of the magnetic air gaps.

According to a thirteenth aspect of the present invention, in therotating electric machine according to the second aspect, the magneticair gaps may be arranged asymmetrically with respect to the q-axispassing through the salient pole center and symmetrically with respectto a d-axis passing through a magnetic pole center of the magnet.

According to a fourteenth aspect of the present invention, in therotating electric machine according to the second aspect, the magneticair gaps may be arranged symmetrically with respect to the q-axispassing through the salient pole center and asymmetrically with respectto a d-axis passing through a magnetic pole center of the magnet.

According to a fifteenth aspect of the present invention, in therotating electric machine according to the first aspect, the rotor mayinclude a plurality of rotor cores each including a laminate ofelectromagnetic steel sheets each provided with a hole or recess thatconstitutes a magnetic air gap.

According to a sixteenth aspect of the present invention, it is possiblein the rotating electric machine according to the fifteenth aspect thateach of the rotor cores has different position of the magnetic air gapdepending on the position in the axial direction by offsetting theelectromagnetic steel sheets in the circumferential direction by a unitof magnetic pole pitch of the magnet.

According to a seventeenth aspect of the present invention, in therotating electric machine according to the second aspect, the rotor mayinclude a first skew structure in which the magnets are arranged offsetin the circumferential direction corresponding to the axial positions ofthe magnets and a second skew structure in which the magnetic air gapsare arranged offset in the circumferential direction corresponding tothe axial positions of the magnetic air gaps.

According to an eighteenth aspect of the present invention, it ispreferred in the rotating electric machine according to the first aspectthat the stator coil is wound by distributed winding.

An electric vehicle according to a nineteenth aspect of the presentinvention includes a rotating electric machine according to the firstaspect; a battery that supplies direct current power; and a conversionunit that converts the direct current power of the battery into analternating current power and supplies the alternating current power tothe rotating electric machine, and utilizes a torque of the rotatingelectric machine as a driving force.

Advantageous Effect of the Invention

According to the present invention, the performance (for example,efficiency, reliability, cost performance, or productivity) of a motorcan be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic construction of a hybrid electric vehiclehaving mounted thereon a rotating electric machine according to oneembodiment of the present invention;

FIG. 2 presents a circuit diagram of the power conversion apparatus 600shown in FIG. 1;

FIG. 3 presents a cross-sectional view of the rotating electric machine200 or 202 shown in FIG. 1;

FIG. 4(a) presents a perspective view of the rotor core 252 shown inFIG. 3;

FIG. 4(b) presents an exploded perspective view of the rotor core 252shown in FIG. 3;

FIG. 5(a) presents a cross-sectional view of the stator 230 and therotor 250 along the A-A line of FIG. 3;

FIG. 5(b) presents a cross-sectional view of the stator 230 and therotor 250 along the B-B line of FIG. 3;

FIG. 6(a) presents an enlarged cross-sectional view near the permanentmagnet 254 b along the A-A line of FIG. 3;

FIG. 6(b) presents an enlarged cross-sectional view near the permanentmagnet 254 b along the B-B line of FIG. 3;

FIG. 7 presents an illustration diagram of reluctance torque;

FIG. 8(a) shows distribution of magnetic fluxes on the A-A cross-sectionwhen power is not applied;

FIG. 8(b) shows distribution of magnetic fluxes of the rotating electricmachine only in the region 401;

FIG. 8(c) shows distribution of magnetic fluxes of the rotating electricmachine only in the region 402;

FIG. 9(a) shows the wave form of cogging torque when power is notapplied;

FIG. 9(b) shows the wave form of induced line voltage when power is notapplied;

FIG. 10(a) shows distribution of magnetic fluxes on the A-Across-section when power is applied;

FIG. 10(b) shows distribution of magnetic fluxes of the rotatingelectric machine only in the region 401;

FIG. 10(c) shows distribution of magnetic fluxes of the rotatingelectric machine only in the region 402;

FIG. 11(a) shows the wave form of torque fluctuations when power isapplied;

FIG. 11(b) shows the wave form of line voltage when power is applied;

FIG. 12 presents a cross-sectional view illustrating a reduction incogging torque, showing a part of each of the stator core 232 and therotor 250;

FIG. 13 presents a diagram showing relationship between the ratio ofmagnetic pole radian τm/τp and cogging torque;

FIG. 14 presents a diagram showing maximum torque when magnetic poleradian ratios τm/τp and τg/τp are changed;

FIG. 15(a) shows cross-sections of the stator 230 and the rotor 250 ofthe surface-magnet type rotating electric machine according to anotherembodiment of the present invention;

FIG. 15(b) shows cross-sections of the stator 230 and the rotor 250 ofthe type of rotating electric machine in which a plurality of magnets isarranged in a V-shape configuration according to another embodiment ofthe present invention;

FIG. 16 shows cross-sections of the stator 230 and the rotor 250according to another embodiment of the present invention;

FIG. 17(a) shows cross-sections of the stator 230 and the rotor 250according to another embodiment;

FIG. 17(b) shows cross-sections of the stator 230 and the rotor 250according to another embodiment;

FIG. 17(c) shows cross-sections of the stator 230 and the rotor 250according to another embodiment;

FIG. 18 presents cross-sectional view of the stator 230 and the rotor250 according to another embodiment in a rotating electric machine withconcentrated winding;

FIG. 19(a) presents a perspective view of the rotor core 252 accordingto another embodiment of the present invention;

FIG. 19(b) presents an exploded perspective view of the rotor core 252according to another embodiment of the present invention;

FIG. 20(a) presents cross-sectional view of the stator 230 and rotor 250along A-A line that passes a part of the core 301;

FIG. 20(b) presents cross-sectional view of the stator 230 and rotor 250along A-A line that passes a part of the core 302;

FIG. 21(a) presents an enlarged cross-sectional view near the permanentmagnet 254 b along the A-A line;

FIG. 21(b) presents an enlarged cross-sectional view near the permanentmagnet 254 b along the B-B line;

FIG. 22(a) shows a surface magnet-type rotating electric machineaccording to another embodiment of the present invention;

FIG. 22(b) shows a rotating electric machine according to anotherembodiment of the present invention in which a plurality of magnets isarranged in a V-shape configuration;

FIG. 23 shows a rotating electric machine provided with two magnetic airgaps 258 for one assisted salient pole 259, showing the stator 230 andthe rotor 250 in cross-section;

FIG. 24(a) presents a cross-sectional view of the stator 230 and therotor 250 according to another embodiment of the present invention;

FIG. 24(b) presents a cross-sectional view of the stator 230 and therotor 250 according to another embodiment of the present invention;

FIG. 24(c) presents a cross-sectional view of the stator 230 and therotor 250 according to another embodiment of the present invention; and

FIG. 25 presents a cross-sectional view of the stator 230 and the rotor250 in a rotating electric machine with concentrated winding.

DESCRIPTION OF EMBODIMENTS

Hereafter, an embodiment of the present invention is explained referringto the attached drawings.

The rotating electric machine according to the present embodiment cansuppress both cogging torque when power is not applied and torquefluctuations when power is applied as will be explained below so that areduction in size, a reduction in cost and reduction in torquefluctuations can be achieved. As a result, the rotating electric machineaccording to the present embodiment is suitable as a motor for drivingan electric vehicle and an electric vehicle that produces low vibrationand low noises and hence giving comfortable ride quality can beprovided. The rotating electric machine can be applied to a genuineelectric vehicle that is driven only by a rotating electric machine andto a hybrid electric vehicle that is driven by both an engine and arotating electric machine. Hereafter, explanation is focused on thehybrid electric vehicle.

First Embodiment

FIG. 1 presents a schematic diagram showing the construction of a hybridelectric vehicle having mounted thereon a rotating electric machineaccording to an embodiment of the present invention. A vehicle 100 hasmounted thereon an engine 120 and a first rotating electric machine 200,a second rotating electric machine 202, and a battery 180. The battery180 supplies direct current power to the rotating electric machines 200and 202 when driving forces of the rotating electric machines 200 and202 are required and the battery 180 receives direct current power fromthe rotating electric machines 200 and 202 upon regenerative driving.Transfer of direct current power between the battery 180 and therotating electric machines 200 and 202 is conducted through a powerconverter unit 600. Though not shown, the vehicle has mounted thereon abattery that supplies low voltage power (for example, 14-volt power) andsupplies direct current power to a control circuit, which is explainedhereinbelow.

The rotation torques by the engine 120 and the rotating electricmachines 200 and 202 are transmitted to a front wheels 110 through atransmission 130 and a differential gear 160. The transmission 130 iscontrolled by a transmission control unit 134 and the engine 120 iscontrolled by an engine control unit 124. The battery 180 is controlledby a battery control unit 184. The transmission control unit 134, theengine control unit 124, the battery control unit 184, the powerconverter unit 600, and an integrated control unit 170 are connected toeach other through communication line 174.

The integrated control unit 170 receives state information indicating astate of each of the control units from the control devices downstreamof the integrated control unit 170, i.e., the transmission control unit134, the engine control unit 124, the power converter unit 600, and thebattery control unit 184 through the communication line 174. Theintegrated control unit 170 calculates a control command for each of thecontrol devices based on the state information. The calculated controlcommands are transmitted to the respective control units through thecommunication circuit 174.

The battery 180, which is at high voltage, comprises a secondary batterysuch as a lithium ion battery or a nickel-metal hydride battery andoutputs direct current power at high voltage in the range of 250 V to600 V or higher. The battery control unit 184 outputs information on astate of discharge of the battery 180 and information on a state of eachunit cell of the battery included in the battery 180 to the integratedcontrol unit 170 through the communication line 174.

The integrated control unit 170 determines whether or not charge of thebattery 180 is necessary based on the state information from the batterycontrol unit 180 and outputs an instruction to perform power-generatingoperation to the power converter unit 600 when the charge of the battery180 is determined to be necessary. The integrated control unit 170 inthe main performs management of output torques of the engine 120 and therotating electric machines 200 and 202, calculation of an integratedtorque and a distribution ratios of torques from the output torque ofthe engine 120 and the output torques of the rotating electric machines200 and 202, and transmission of control commands based on results ofthe calculation to the transmission control unit 134, the engine controlunit 124, and the power converter unit 600. The power converter unit 600controls the rotating electric machines 200 and 202 to generate thetorque output or generated power energy as commanded based on the torquecommand from the integrated control unit 170.

The power converter unit 600 is provided with a power semiconductor thatconstitutes an inverter for driving the rotating electric machines 200and 202. The power converter unit 600 controls a switching operation ofthe power semiconductor based on the command from the integrated controlunit 170. The rotating electric machines 200 and 202 are operated aselectric machines or alternators by the switching operation of the powersemiconductor.

When the rotating electric machines 200 and 202 are operated as electricmachines, direct current power from the high voltage battery 180 issupplied to direct current terminals of the inverter in the powerconverter unit 600. The power converter unit 600 converts supplieddirect current power into three-phase alternating current power bycontrolling the switching operation of the power semiconductor andsupplies the obtained alternating current power to the rotating electricmachines 200 and 202. On the other hand, when the rotating electricmachines 200 and 202 are operated as alternators, the rotors of therotating electric machines 200 and 202 are driven and rotated byrotating torque applied from outside to generate three-phase alternatingcurrent power in stator windings of the rotating electric machines 200and 202. The generated three-phase alternating current power isconverted into direct current power by the power converter unit 600. Theobtained direct current power is supplied to the high voltage battery180 to effect charging.

FIG. 2 presents a circuit diagram of the power converter unit 600 shownin FIG. 1. The power converter unit 600 is provided with a firstinverter unit for the rotating electric machine 200 and a secondinverter unit for the rotating electric machine 202. The first inverterunit includes a power module 610, a first drive circuit 652 thatcontrols the switching operation of each power semiconductor 21 in thepower module 610, and a current sensor 660 that detects current in therotating electric machine 200. The drive circuit 652 is provided on adrive circuit board 650. On the other hand, the second inverter unitincludes a power module 620, a second drive circuit 656 that controlsthe switching operation of each power semiconductor 21 in the powermodule 620, and a current sensor 662 that detects current in therotating electric machine 202. The drive circuit 656 is provided on adrive circuit board 654. A control circuit 648 provided on a controlcircuit board 646, a capacitor module 630, and a transmitting andreceiving circuit 644 implemented in a connector board 642 are used incommon by the first and the second inverter units.

The power modules 610 and 620 operate in response to corresponding drivesignals output from the drive circuits 652 and 656, respectively. Thepower modules 610 and 620 convert direct current power supplied from thebattery 180 into three-phase alternating current power and supplies theobtained power to stator coils, which are armature coils of thecorresponding rotating electric machines 200 and 202, respectively. Thepower modules 610 and 620 convert the alternating current power inducedin the stator coils of the rotating electric machines 200 and 202 intodirect current power and then supply the resultant direct current powerto the high voltage battery 180.

The power modules 610 and 620 include a three-phase bridge circuit asshown in FIG. 2. Series circuits corresponding to the three-phases areeach electrically connected in parallel between the positive electrodeside and the negative electrode side of the battery 180. Each of theseries circuits includes a power semiconductor 21 constituting an upperarm and a power semiconductor 21 constituting a lower arm. The powersemiconductors 21 are connected to each other in series. The powermodule 610 and the power module 620 have substantially the same circuitconstruction as shown in FIG. 2. Here, the power module 610 is explainedon behalf of the both.

In the present embodiment, IGBT (Insulated Gate Bipolar Transistor) 21is used as the power semiconductor for switching. IGBT 21 includes threeelectrodes, i.e., a collector electrode, an emitter electrode, and agate electrode. Between the collector electrode and the emitterelectrode of IGBT 21 is electrically connected a diode 38. The diode 38includes two electrodes, i.e., a cathode and an anode. The cathode andanode are electrically connected to the collector electrode and emitterelectrode, respectively, of IGBT 21 so that a direction of from theemitter electrode to the collector electrode of the IGBT 21 is a forwarddirection.

Also, MOSFET (Metal Oxide Semiconductor Field-Effect Transistor) may beused as the power semiconductor for switching. MOSFET includes threeelectrodes, i.e., a drain electrode, a source electrode, and a gateelectrode. Since MOSFET includes a parasite diode between the sourceelectrode and the drain electrode so that a direction of from the drainelectrode to the source electrode is a forward direction, it is notnecessary that MOSFET includes the diode 38 as shown in FIG. 2.

The arms for respective phases each include the source electrode of IGBT21 and the drain electrode of IGBT 21 electrically connected to eachother in series. In the present embodiment, only a single IGBT is shownfor each of the upper and lower arms for each phase. In actuality, aplurality of IGBTs is electrically connected in parallel since currentcapacity to be controlled is huge. Hereafter, a single powersemiconductor is described in order to make explanation simpler.

In the example shown in FIG. 2, each of the upper and lower arms foreach phase includes three IGBTs. The drain electrode of IGBT 21 in eachupper arm for each phase and the source electrode of IGBT 21 in eachlower arm for each phase are electrically connected to the positiveelectrode side and the negative electrode side, respectively, of thebattery 180. Middle points of respective arms for each phase (aconnection part between the source electrode of the upper arm side IGBTand the drain electrode of the lower arm side IGBT) are electricallyconnected to the armature coils (stator coils) of the correspondingphase of the corresponding rotating electric machines 200 and 202.

The drive circuits 652 and 656 constitute respective drive units forcontrolling the corresponding power modules 610 and 620 and generatedrive signals for driving IGBTs 21 based on the control signals outputfrom the control circuit 648. The drive signals generated in the drivecircuits 652 and 656 are output to the gate of each power semiconductorin the power modules 610 and 620. The drive circuits 652 and 656 areeach provided with six integrated circuits that generate drive signalssupplied to the respective gates of the upper and lower arms for eachphase. The six integrated circuits are formed as one block.

The control circuit 648 constitutes the control unit in each of thepower modules 610 and 620. The control circuit 648 comprises amicrocomputer that calculates control signals (control values) foroperating (turning on or off) the plurality of power semiconductors forswitching. Torque command signals (torque command values) from asuperordinate control unit, sensor outputs from the current sensors 660and 662, and sensor outputs from the rotation sensors mounted on therotating electric machines 200 and 202 are input to the control circuit648. The control circuit 648 calculates control values based on theinput signals and outputs control signals for controlling the switchingtiming to the drive circuits 652 and 656.

The transmitting and receiving circuit 644 implemented on the connectorboard 624 is to connect the power converter unit 600 and an outercontrol unit, and transmits and receives information with other unitsthrough the communication line 174 as shown in FIG. 1. The capacitormodule 630 constitutes a smoothing circuit for suppressing a fluctuationin direct current voltage generated by the switching operation of IGBT21 and is electrically connected in parallel to the terminal on thedirect current side in the first power module 610 and the second powermodule 620.

FIG. 3 presents a cross-sectional view of the rotating electric machine200 or 202 shown in FIG. 1. The rotating electric machines 200 and 202have substantially the same structures. Hereafter, explanation is madetaking the structure of the rotating electric machine 200 as arepresentative example. The structure explained hereafter does not haveto be adopted in both of the rotating electric machines 200 and 202 butit will be sufficient if it is adopted at least one of them.

Inside a housing 212, there is held the stator 230. The stator 230includes the stator core 232 and the stator coil 238. The rotor 250 isrotatably held inside the stator core 232 with an air gap 222. The rotor250 includes the rotor core 252, permanent magnets 254, and nonmagneticwear plates 226. The rotor core 252 is fixed to a shaft 218. The housing212 has a pair of end brackets 214 each provided with a bearing 216. Theshaft 218 is rotatably held by these bearings 216.

As shown in FIG. 3, the shaft 218 is provided with a resolver 224 thatdetects the positions of the poles of the rotor 250 and rotation speedof the rotor 250. An output from the resolver 224 is introduced into thecontrol circuit 648 shown in FIG. 2. The control circuit 648 outputs thecontrol signals to the drive circuit 652 based on the introduced output.The drive circuit 652 outputs the drive signals to the power module 610based on the control signals. The power module 610 performs switchingoperation based on the control signals to convert the direct currentpower supplied from the battery 180 into three-phase alternating currentpower. The three-phase alternating current power is supplied to thestator coil 238 and a rotating magnetic field is generated in the stator230. The frequency of the three-phase alternating current is controlledbased on the detected value by the resolver 224. Also, the phases of thethree-phase alternating current are controlled based on the detectedvalue by the resolver 224.

FIG. 4(a) presents a perspective view of the rotor core 252 of the rotor250. The rotor core 252 includes two cores 301 and 302 as shown in FIG.4(b).The length H2 of the core 302 along its axial direction is set tobe substantially the same as the length H1 of the core 301 along itsaxial direction. FIGS. 5(a) and 5(b) show the stator 230 and the rotor250 in cross-section. FIG. 5(a) presents a cross-sectional view alongthe A-A line passing through a part of the core 301 (see, FIG. 3). FIG.5(b) presents a cross-sectional view along the B-B line passing througha part of the core 302 (see, FIG. 3). In FIGS. 5(a) and 5(b), depictionof the housing 212, the shaft 218, and the stator coil 238 is omitted.

On the inner periphery side of the stator core 232, there are uniformlyarranged a number of slots 24 and teeth 236 all around. In FIGS. 5(a)and 5(b), not all of the slots and teeth have been allotted referencenumerals but only some of the teeth and slots have been allottedreference numerals on behalf of the whole. In the slot 24, a slotinsulator (not shown) is provided and a plurality of phase winding wiresof u-phase to w-phase is fitted. In the present embodiment, distributedwinding is adopted as the method of winding the stator coil 238.

The distributed winding is a method of winding a coil wire by which thewire is wound around the stator core 232 such that the phase windingwire is accommodated in two slots that are remotely arranged over aplurality of slots 24 intervening therebetween. In the presentembodiment, the distributed winding is adopted as the method of wirewinding, so that the formed distribution of magnetic flux is nearlysinusoidal, with the result that reluctance torque can be easilyobtained. Therefore, control of the rotation speed over a wide range ofthe number of rotations ranging from low rotation speed to high rotationspeed can be achieved by utilizing field weakening control andreluctance torque. The distributed winding is suitable for obtainingmotor characteristics adapted for electric vehicles.

Each of the cores 301 and 302 of the rotor core 252 is provided withholes 310 in each of which a rectangular magnet is to be inserted. Thepermanent magnets 254 are introduced into the holes 310 and fixedthereto with an adhesive or the like. The widths of the holes 310 in thecircumferential direction are set to be larger than the widths of thepermanent magnets 254 in the circumferential direction. On both sides ofthe permanent magnets 254 are formed magnetic air gaps 257. The magneticair gaps 257 may be filled with the adhesive. Alternatively, themagnetic air gaps 257 may be filled with forming resins together withthe permanent magnets 254, which will then be integrally fixed. Thepermanent magnets 254 operate as field poles of the rotor 250.

The directions of magnetization of the permanent magnets 254 are setalong the radial direction of the rotor core 252 and reversed everyfield pole. That is, assuming that the surface of a permanent magnet 254a on the stator side is an N pole and a surface of the permanent magnet254 a on the axis side is an S pole, a surface of an adjacent permanentmagnet 254 b on the stator side is an S pole and a surface of thepermanent magnet 254 b on the axis side is an N pole. The permanentmagnets 254 a and 254 b are arranged alternately in the circumferentialdirection. In the present embodiment, twelve of such permanent magnets254 are arranged at regular intervals. Thus, the rotor 250 has twelvepoles.

The permanent magnets 254 may either be embedded in the rotor core 252after magnetization or be inserted in the rotor core 252 beforemagnetization and then magnetized by applying thereto a strong magneticfield. Since the permanent magnets 254 after the magnetization arestrong magnets, if the permanent magnets 254 are magnetized before theyare fixed to the rotor 250, strong attractive forces are generatedbetween the rotor core 252 and the permanent magnets 254 when thepermanent magnets 254 are fixed and the resulting centripetal forcesprevent the operation for producing the rotor. In addition, dust such asiron powder may adhere to the permanent magnets 254 due to the strongattractive forces. Therefore, the method in which magnetization isperformed after the permanent magnets 254 have been inserted into therotor core 252 is more productive than otherwise.

The permanent magnets 254 may include sintered magnets containingneodymium or samarium, ferrite magnets, bond magnets containingneodymium, and so on. The permanent magnets 254 have a residual magneticflux density of approximately 0.4 to 1.3 T.

FIG. 6(a) presents an enlarged view of a part of the cross-sectionalview shown in FIG. 5(a). The core 301 of the rotor core 252 is providedwith grooves that constitute magnetic air gaps 258 on a surface of therotor 250 in addition to the magnetic air gaps 257 formed on both thesides of the permanent magnets 254. The magnetic air gaps 257 areprovided to reduce cogging torque and the magnetic air gaps 258 areprovided to reduce torque fluctuations when power is applied. Assumingthat as seen from the inner periphery of the rotor 250, a central axisbetween the permanent magnet 254 a and a next magnet on the left side ofthe permanent magnet 254 a is named q-axis a and a central axis betweenthe permanent magnet 254 b and a next magnet on the left side of thepermanent magnet 254 b is named q-axis b, a magnetic air gap 258 a isarranged offset to the right with respect to the q-axis a and a magneticair gap 258 b is arranged offset to the left with respect to the q-axisb. The magnetic air gap 258 a and the magnetic air gap 258 b arearranged symmetric with respect to a d-axis, which is a central axis ofmagnetic poles.

On the other hand, FIG. 6(b) is an enlarged view of a part of thecross-sectional view shown in FIG. 5(b). The core 302 of the rotor core252 is formed of magnetic air gaps 258 c and 258 d instead of themagnetic air gaps 258 a and 258 b. As seen from the inner periphery ofthe rotor 250, the magnetic air gap 258 c is arranged offset to the leftwith respect to the q-axis a and the magnetic air gap 258 d is arrangedoffset to the right with respect to the q-axis b. From FIGS. 5(a), 5(b),6(a), and 6(b), it can be seen that the cross-sectional shapes of thecores 301 and 302 are the same except that the positions at which themagnetic air gaps 258 a and 258 b and the magnetic air gaps 258 c and258 d are different, respectively.

The magnetic air gaps 258 a and 258 d are arranged at positions offsetfrom each other by 180 degrees in electric angle and the magnetic airgaps 258 b and 258 c are arranged at positions offset from each other by180 degrees in electric angle. That is, the core 302 can be formed byrotating the core 301 by one pitch of magnetic poles. As a result, thecore 301 and the core 302 can be produced using the same mold so thattheir production cost can be decreased. The circumferential positions ofthe holes 310 of the cores 301 and 302 correspond to each other withoutany offset. As a result, the permanent magnet 254 fitted in each hole310 constitute an integrated magnet penetrating each of the cores 301and 302 without being divided in the axial direction. Of course, aplurality of divided magnets 254 may be arranged as being stacked in theaxial direction of the hole 310.

When a rotating magnetic field is generated in the stator 230 by thethree-phase alternating current, the rotating magnetic field interactswith the permanent magnets 254 a and 254 b of the rotor 250 to generatea magnet torque. The rotor 250 is affected by a reluctance torque inaddition to the magnet torque.

FIG. 7 presents a diagram illustrating a reluctance torque. Generally,an axis along which magnetic flux passes through the center of a magnetis called a d-axis and an axis along which magnetic flux passes oneinterpolar position to another interpolar position is called a q-axis.The part of the core that is present at the center between the poles ofthe magnet is called an assisted salient pole member 259. Thepermeability of the permanent magnet 254 provided in the rotor 250 isapproximately the same as that of air, so that when viewed from the sideof the stator, the d-axis member is magnetically concave and the q-axismember is magnetically convex. Therefore, the part of the core in theq-axis part is called salient pole. The reluctance torque is generatedby a difference in readiness of transmission of magnetic flux along theaxis between the d-axis and the q-axis, i.e., by a salient pole ratio.

As mentioned above, the rotating electric machine to which the presentembodiment is applied is one that utilizes both a magnet torque and anassisted salient pole reluctance torque. Both the magnet torque and thereluctance torque each generate torque fluctuations. The torquefluctuations include a fluctuation component that is generated whenpower is not applied and a fluctuation component that is generated whenpower is applied. The fluctuation component that is generated when poweris not applied is generally called cogging torque. When the rotatingelectric machine is actually used in a loaded state, there are generatedcombined torque fluctuations consisting of the cogging torque and thefluctuation component when power is applied.

Most conventional methods for reducing the torque fluctuations of such arotating electric machine relate to a reduction in cogging torque onlybut disclose nothing about a reduction in torque fluctuations occurringwhen power is applied. However, in many cases, noises of the rotatingelectric machine occur not in an unloaded state but in a loaded state.That is, it is important to reduce torque fluctuations in a loaded statein order to reduce noises of the rotating electric machine. Anycountermeasure that relates to cope with the cogging torque only isinsufficient.

Now, the method of reducing torque fluctuations according to the presentembodiment is explained.

First, influence of the magnetic air gap 258 when power is not applied.FIG. 8(a) shows a result of simulation of distribution of magnetic fluxwhen current is not flown in the stator coil 238, that is, distributionof magnetic flux by the permanent magnet 254. FIG. 8(a) shows two poles,i.e., a region 401 constituted by the permanent magnet 254 a and aregion 402 constituted by the permanent magnet 254 b. That is, theabove-mentioned result is a result of simulation of the rotatingelectric machine in which the region 401 and the region 402 are arrangedalternately in the circumferential direction, showing an A-Across-section. Since the rotating electric machine according to thepresent embodiment includes 12 poles, the regions 401 and 402 eachinclude 6 poles, which are alternately arranged in the circumferentialdirection. For each pole, the magnetic air gaps 258 a and 258 b are inthe assisted salient pole member 259 in the region 401 but the assistedsalient pole member 259 in the region 402 includes no magnetic air gap258.

When power is applied, the magnetic flux by the permanent magnet 254 isshort-circuiting the magnet ends. Therefore, no magnetic flux at allpasses along the q-axis. It can be seen that substantially no magneticflux passes through portions of the magnetic air gaps 258 a and 258 bprovided at positions slightly offset from the magnetic air gaps 257 inthe magnet ends. The magnetic flux passing the stator core 232 passes apart of the core on the side of the stator in the permanent magnet 254to reach the teeth 236. As a result, the magnetic air gaps 258 a and 258b give substantially no influence on the magnetic flux when power is notapplied that relates to cogging torque. From this, it follows that themagnetic air gaps 258 a and 258 b give no influence on the coggingtorque.

FIG. 8(b) shows the result of simulation on the region 401 only and FIG.8(c) shows the result of simulation on the region 402 only. FIG. 8(b)shows a rotating electric machine that includes twelve poles eachconsisting of the region 401 only arranged in the circumferentialdirection and is constructed such that the direction of magnetization ofthe permanent magnet 254 of each pole is reversed pole by pole. FIG.8(c) shows a rotating electric machine that includes twelve poles eachconsisting of the region 402 only arranged in the circumferentialdirection and is constructed such that the direction of magnetization ofthe permanent magnet 254 of each pole is reversed pole by pole. FIGS.8(b) and 8(c) each show similar magnetic flux distribution to that shownin FIG. 8(a), with no magnetic flux passing along the q-axis.

FIG. 9(a) shows the waveform of cogging torque. FIG. 9(b) shows awaveform of induced line voltage that occurs on the side of the statorwhen the rotor 250 rotates. The horizontal axis shows the rotation angleof the rotor in electric angle. Line L11 shows the case of the rotorshown in FIG. 8(a) in which the region 401 having the magnetic air gaps258 and the region 402 having no magnetic air gap 258 are alternatelyarranged. Line 12 shows the rotating electric machine shown in FIG. 8(b)in which only the region 401 having the magnetic air gaps 258 isarranged. Line 13 shows the case of the rotating electric machine shownin FIG. 8(c) in which only the region 402 having no magnetic air gap 258is arranged. The result shown in FIG. 9(a) indicates that presence orabsence of the magnetic air gaps 258 gives substantially no influence onthe cogging torque.

The induced voltage is a voltage generated when the magnetic flux of therotating rotor 250 forms flux linkage with the stator coil 238. As shownin FIG. 9(b), it is understood that the induced voltage waveform is notinfluenced by the presence or absence of the magnetic air gaps 258. Theinduced voltage indicates reflection of the magnetic flux of a magnet inthe result of simulations shown in FIGS. 8(a), 8(b), and 8(c). That theinduced voltage is not changed means that the magnetic air gaps 258 givesubstantially no influence on the magnetic flux of the magnet.

Now, influences of the magnetic air gap 258 when power is applied areexplained. FIGS. 10(a), 10(b), and 10(c) each show the result ofsimulation of magnetic flux distribution when power is applied to thestator coil 238. FIG. 10(a) shows the result of simulation on therotating electric machine similar to one shown in FIG. 8(a). FIG. 10(b)shows the result of simulation on the rotating electric machine similarto one shown in FIG. 8(b). FIG. 10(c) shows the result of simulation onthe rotating electric machine similar to one shown in FIG. 8(c). Therotating electric machine according to the present embodiment is a motorincluding 6 slots per pole. A coil 233 of the stator coil 238 providedin the slot 24 of the stator coil 232 is branched into two layers in thedirection of the depth of the slot. The coil 233 arranged on the bottomside of the slot is a short pitch winding that is inserted into therotor side of the slot 24 skipping over six slots consisting of first tofifth slots assuming that the next slot is taken as first slot. The sortpitch winding is featured in that it can reduce harmonics in themagnetomotive force of the stator, shorten the coil end, and reducecopper loss. The winding for reducing harmonics can minimize sixth-ordertorque fluctuations specific to three-phase motors and substantiallyonly nearly twelfth components remain.

Referring to FIGS. 10(a), 10(b) and 10(c), the magnetic flux flows alongthe q-axis in any of the simulation results. This is because the currentin the stator 230 forms a magnetic flux in the q-axis. Comparing FIGS.10(a) and 10(b) with FIG. 10(c) in which no magnetic air gap 258 ispresent, it can be seen that in FIGS. 10(a) and 10(b), the magnetic airgap 258 changes the flow of magnetic flux of the assisted salient polemember 259. Therefore, the magnetic air gap 258 that is present in theassisted salient pole member 259 gives magnetic influences only whenpower is applied.

FIG. 11(a) shows the torque waveform when power is applied and FIG.11(b) shows the waveform of line voltage when power is applied. Thehorizontal axis indicates the rotation angle of the rotor in electricangle. Line L21 indicates the case of the rotor shown in FIG. 10(a) inwhich the region 401 having the magnetic air gaps 258 and the region 402having no magnetic air gap 258 are alternately arranged. Line 22 showsthe rotating electric machine shown in FIG. 10(b) in which only theregion 401 having the magnetic air gaps 258 is arranged. Line 23 showsthe case of the rotating electric machine shown in FIG. 10(c) in whichonly the region 402 having no magnetic air gap 258 is arranged.

FIG. 11(a) indicates that in the rotating electric machine according tothe present embodiment, twelfth-order torque fluctuation component,i.e., component of 30 degrees period in electric angle is dominant butsixth-order component is almost null. Both L21 and L22 have changedwaveforms of torque fluctuations as compared with the torquefluctuations L23 in the case where the magnetic air gap 258 is notformed, that is only the region 402 is present. This indicates that themagnetic flux when power is applied is influenced by the magnetic airgap 258. Further, the torque fluctuations L22 of the rotating electricmachine including only the region 401 and the torque fluctuations L23 ofthe rotating electric machine including only the region 402 areapproximately opposite in phase to each other. As shown in FIG. 10(a),the rotating electric machine according to the present embodiment has aconstruction in which the region 401 and the region 402 are alternatelyarranged and as indicated by the torque fluctuations L21, sum of thetorque fluctuations that is received by the rotor in whole is a meanvalue of the torque fluctuations L22 and the torque fluctuations L23.

As mentioned above, in the present embodiment, provision of the magneticair gaps 258 a and 258 b enables reduction of torque fluctuations whenpower is applied. To obtain such an effect, it is preferred that thewidth angles (angles in the circumferential direction) of the groovesthat constitute the magnetic air gaps 258 are set to be within the rangeof ¼ to ½ of the pitch angle of the teeth 236. Two or more types of themagnetic air gaps 258 may be used to form the assisted salient polemember 259. Thereby, it is becomes more freely to reduce torquefluctuations so that reduction of fluctuations can be performed moreprecisely.

A further feature is that as the torque is not decreased more than thecase where no magnetic air gap is provided. In the case of the structurecalled “skew” conventionally adopted to reduce torque fluctuations,skewing results in a decrease in torque, which prevents size reduction.However, the present embodiment is featured that not only it is possibleto reduce the torque fluctuations when power is applied independently ofthe cogging torque but also the torque itself is not decreased. This isbecause the torque fluctuations in the case of the original groove-lessrotor dominantly include the twelfth-order component. It is effectivethat the stator coil is made of a short pitch winding.

Also, it can be seen that the voltage when power is applied isinfluenced by presence or absence of the magnetic air gap 258 as shownin FIG. 11(b). In this case, there occurs a potential difference betweenthe winding of each phase of the stator coil 238 facing the rotor 250 inthe region 401 and the winding of each phase of the stator coil 238facing the rotor 250 in the region 402, so that when the windingsseparately for each phase are connected in parallel, circulation currentflows to increase loss. As shown in FIG. 6, the rotating electricmachine according to the present embodiment has the core 302 formed byrotating the core 301 by one pitch of magnetic pole and the axiallengths of the cores 301 and 302 are set to substantially the same asshown in FIG. 4(b). As a result, the voltage that occurs in the windingof each phase of the stator coil 238 facing each pole can be madesubstantially the same, so that substantially no circulation currentflows. However, when windings of respective phases of the stator coil238 facing the rotor 250 in the regions 401 and 402 are connected toeach other in series, substantially no circulation current flows, sothat a construction with only the core 301 or 302 may also be adopted.

As mentioned above, if the magnetic air gaps 258 a and 258 b are formed,this does not give any influence on the cogging torque when power isapplied. Therefore, the cogging torque can be reduced separately fromthe reduction of the torque fluctuations when power is applied, byapplying a method of reducing the cogging torque as conventionally used.In the present embodiment, reduction of cogging torque is achieved byadopting the following construction.

FIGS. 12 and 13 present diagrams illustrating the method of reducingcogging torques. FIG. 12 presents a cross-sectional view showing therotor 250 and a part of the stator core 232. In FIG. 12, τp indicatespole pitch of the permanent magnet 254 and τm indicates width angle ofthe permanent magnet 254. On the other hand, τg indicates an angle forthe permanent magnet 254 and the magnetic air gaps 257 on both sidesthereof, i.e., a width angle of the hole 310 shown in FIG. 4. Byadjusting ratios of these angles τm/τp and τg/τp, cogging torques can bereduced. In the present embodiment, τm/τp is called magnet pole radianand τg/τp is called magnet hole pole radian.

FIG. 13 presents a diagram showing relationship between the ratio ofτm/τp and cogging torque. The result shown in FIG. 13 relates to thecase where τm=τg and the permanent magnet 254 and the magnetic air gap257 are in the form of arc concentric to the outer periphery of therotor 250. In the case where rectangular magnets are used as in thepresent embodiment, optimum values are somewhat varied. However,needless to say, the same idea is used. In FIG. 13, the horizontal axisindicates amplitude of cogging torque and the horizontal axis indicatesrotation angle of the rotor 250 in electric angle. The magnitude ofamplitude of fluctuations varies depending on the magnitude of the ratioτm/τp. When τm=τg, selecting τm/τp at about 0.75, the cogging torque canbe reduced. The tendency that the cogging torque is not changed by themagnetic air gaps 258 shown in FIG. 9(a) makes it possible to applyratio of the width of magnet to the pitch of pole τm/τp, to any wheresimilarly. As a result, by designing the shape of the rotor 250 to beone shown in FIG. 5 under the above-mentioned conditions, both thecogging torque and the torque fluctuations when power is applied can bereduced.

In the example shown in FIG. 13, explanation has been made assumingτm=τg. However, to efficiently utilize the reluctance torque which is aneffect of the assisted salient pole member 259, the magnet hole poleradian τg/τp may advantageously be set to about 0.5 to about 0.9,preferably about 0.7 to about 0.8.

FIG. 14 is an example of calculation of maximum torque when the magnetpole radian τm/τp and the magnet hole pole radian τg/τp are varied.Similarly to FIG. 13, the permanent magnet 254 and the magnetic air gap257 are in the form of a sector concentric to the outer periphery of therotor 250. The horizontal axis indicates the magnet hole pole radianτg/τp. That this value is 0.7 indicates that the ratio of the assistedsalient pole member 259 to the interpolar pitch is 0.3. Here, the magnetwidth τm cannot be made larger than the opening angle τm of the magnethole, and hence, there is obtained: τg≧τm. An increase in τm results inan increase in width of the permanent magnet 254, so that torqueincreases accordingly. On the other hand, when τm is constant, τg has anoptimal value; when τg/τp is about 0.7 to about 0.8, the maximum torqueis largest. This is because the size of the assisted salient pole member259 has an appropriate value and if τg is made too large or too small ascompared with that value, reluctance torque becomes too small. When τmis larger than 0.75, τm=τg is desirable so that the assisted salientpole member 259 can be as large as possible.

As mentioned above, the reluctance torque can be most efficientlyutilized when τg/τp is set to about 0.7 to about 0.8 and the permanentmagnet 254 can be made smaller. When a rare earth sintered magnet isused as the permanent magnet 254, it is required to use a most efficientamount of magnet since such a magnet is very expensive as compared withother materials. Since the permanent magnet 254 is reduced in size, theinduced voltage by the magnetic flux of the permanent magnet 254 can bereduced, so that the rotating electric machine can be rotated at higherspeeds. Therefore, the rotating electric machine that utilizesreluctance torque as in the present embodiment is generally used inelectric vehicles.

Second Embodiment

FIGS. 15(a) and 15(b) show a rotor according to another embodiment ofthe present invention. The present embodiment is the same as the firstembodiment excepting what is explained hereafter.

FIG. 15(a) shows a rotor of the surface magnet type and FIG. 15(b) showsa rotor in which a plurality of magnets is arranged in a V-shape. Ineither type of the rotor, the assisted salient pole member 259 isbetween any two adjacent permanent magnets 254 and the magnetic air gap258 is arranged in the assisted salient pole member 259. Assuming thatas seen from the inner periphery of the rotor 250, a central axisbetween the permanent magnet 254 a and a next magnet on the left side ofthe permanent magnet 254 a is named q-axis a and a central axis betweenthe permanent magnet 254 b and a next magnet on the left side of thepermanent magnet 254 b is named q-axis b, the magnetic air gap 258 a isarranged offset to the right with respect to the q-axis a and themagnetic air gap 258 b is arranged offset to the left with respect tothe q-axis b. The magnetic air gap 258 a and the magnetic air gap 258 bare arranged symmetric with respect to a d-axis, which is a central axisof the magnetic pole. FIGS. 15(a) and 15(b) show A-A cross-sections ofthe rotor. Similarly to the above-mentioned embodiment, the B-Bcross-section has a shape formed by rotating the shape of the A-Across-section by one pitch of magnetic pole. As explained abovereferring to FIGS. 8(a), 8(b), and 8(c), the reduction of the torquefluctuations in the present embodiment is not affected by the magneticflux of the magnet, so that it does not depend on the shape of themagnet.

Third Embodiment

FIG. 16 illustrates achievement of reduction of torque fluctuations byproviding two magnetic air gaps 258 for each assisted salient polemember 259 according to the present embodiment.

This shape is as follows. Assuming that as seen from the inner peripheryof the rotor 250, a central axis between the permanent magnet 254 a anda next magnet on the left side of the permanent magnet 254 a is namedq-axis a and a central axis between the permanent magnet 254 b and anext magnet on the left side of the permanent magnet 254 b is namedq-axis b, the magnetic air gap 258 a on the right side with respect tothe q-axis a is larger and the magnetic air gap 258 e on the left sidewith respect to the q-axis b is smaller. The magnetic air gap 258 b onthe right side with respect to the q-axis b is larger and the magneticair gap 258 f on the left side with respect to the q-axis b is smaller.The magnetic air gaps 258 a and 258 b and the magnetic air gaps 258 eand 258 f are arranged symmetric with respect to a d-axis, which is acentral axis of the magnetic pole. FIG. 16 shows an A-A cross-section ofthe rotor. Similarly to the above-mentioned embodiment, the B-Bcross-section has a shape formed by rotating the shape of the A-Across-section by one pitch of magnetic pole. Other details than theabove-mentioned are the same as the first embodiment.

Fourth Embodiment

In the examples shown in FIGS. 5(a), 5(b), 15(a), 15(b), and 16, themagnetic air gap 258 is constituted by a groove provided in an outerperiphery of the rotor 250. However, the magnetic air gap 258 may beconstituted by a hole in the assisted salient pole member 259 as shownin FIG. 17(a). The magnetic air gap 257 and the magnetic air gap 258 maybe integrated as shown in FIG. 17(b). The magnetic air gap 258 may beachieved by providing the assisted salient pole member 259 with a regionthat has a different permeability than the rest as shown in FIG. 17(c).In FIG. 17(c), the permeability of the assisted salient pole member 259a is set to be lower than that of the assisted salient pole member 259b. Other details than the above-mentioned are the same as the firstembodiment.

Fifth Embodiment

FIG. 18 illustrates the case where the stator coil 238 shown in FIGS.5(a) and 5(b) is made of the concentrated winding type. The torquefluctuations in the present embodiment depends on the shape of the rotor250 and hence the torque fluctuations can be reduced in the case of theconcentrated winding type, which is a different winding method on thestator side, similarly to what is described above. Other details thanthe above-mentioned are the same as the first embodiment.

Sixth Embodiment

FIG. 19(a) presents a perspective view showing the rotor core 252 of therotor 250 according to another embodiment of the present invention.Other details than the above-mentioned are the same as the firstembodiment.

The rotor core 252 includes two cores 301 and 302 as shown in FIG.19(b). The length H2 of the core 302 in the axial direction is set to beapproximately the same as the length H1 of the core 301 in the axialdirection. FIGS. 20(a) and 20(b) each present a cross-sectional view ofthe stator 230 and the rotor 250. FIG. 20(a) presents an A-Across-sectional view passing a part of the core 301 (see FIG. 3), andFIG. 20(b) presents an B-B cross-sectional view passing a part of thecore 302 (see FIG. 3). In FIGS. 20(a) and 20(b), depiction of thehousing 212, the shaft 218, and the stator coil 238 is omitted.

On the inner periphery side of the stator core 232, there are uniformlyarranged a number of slots 24 and teeth 236 all around. In FIG. 20, notall the slots and teeth are allotted reference numerals but only some ofthe teeth and slots are allotted reference numerals on behalf of thewhole. In the slot 24, a slot insulator (not shown) is provided and aplurality of phase winding wires of u-phase to w-phase is fitted. In thepresent embodiment, distributed winding is adopted as the method ofwinding the stator coil 238.

Each of the cores 301 and 302 of the rotor core 252 is provided withholes 310 in each of which a rectangular magnet is to be inserted. Thepermanent magnets 254 are introduced into the holes 310 and fixedthereto with an adhesive or the like. The widths of the holes 310 in thecircumferential direction are set to be larger than the widths of thepermanent magnets 254 in the circumferential direction. On both sides ofthe permanent magnets 254 are formed magnetic air gaps 257. The magneticair gaps 257 may be filled with the adhesive. Alternatively, themagnetic air gaps 257 may be filled with forming resins together withthe permanent magnets 254, which will then be integrally fixed. Thepermanent magnets 254 operates as a field pole of the rotor 250.

The directions of magnetization of the permanent magnets 254 are setalong the radial direction of the rotor core 252 and reversed everyfield pole. That is, assuming that the surface of a permanent magnet 254a on the stator side is an N pole and a surface of the permanent magnet254 a on the axis side is an S pole, a surface of an adjacent permanentmagnet 254 b on the stator side is an S pole and a surface of thepermanent magnet 254 b on the axis side is an N pole. The permanentmagnets 254 a and 254 b are arranged alternately in the circumferentialdirection. In the present embodiment, twelve of such permanent magnets254 are arranged at regular intervals. Thus, the rotor 250 has twelvepoles.

FIG. 21(a) presents an enlarged view of a part of the cross-sectionalview shown in FIG. 20(a). The core 301 of the rotor core 252 is providedwith grooves that constitute magnetic air gaps 258 on a surface of therotor 250 in addition to the magnetic air gaps 257 formed on both thesides of the permanent magnets 254. The magnetic air gaps 257 areprovided to reduce cogging torque and the magnetic air gaps 258 areprovided to reduce torque fluctuations when power is applied. Assumingthat as seen from the inner periphery of the rotor 250, a central axisbetween the permanent magnet 254 a and a next magnet on the left side ofthe permanent magnet 254 a is named q-axis a and a central axis betweenthe permanent magnet 254 b and a next magnet on the left side of thepermanent magnet 254 b is named q-axis b, a magnetic air gap 258 a isarranged offset to the right with respect to the q-axis a and a magneticair gap 258 b is arranged offset to the left with respect to the q-axisb. There is provided no magnetic air gap on both sides of the q-axis b.The magnetic air gap 258 a and the magnetic air gap 258 b are arrangedsymmetric with respect to a d-axis, which is a central axis of magneticpoles.

On the other hand, FIG. 21(b) is an enlarged view of a part of thecross-sectional view shown in FIG. 20(b). In case of the core 302 of therotor core 252, magnetic air gaps 258 c and 258 d are formed instead ofthe magnetic air gaps 258 a and 258 b. As seen from the inner peripheryof the rotor 250, the magnetic air gap 258 c is arranged offset to theleft with respect to the q-axis a and the magnetic air gap 258 d isarranged offset to the right with respect to the q-axis b. There is nomagnetic air gap on both sides of the q-axis a. From FIGS. 20(a), 20(b),21(a), and 21(b), it can be seen that the cross-sectional shapes of thecores 301 and 302 are the same except that the positions at which themagnetic air gaps 258 a and 258 b and the magnetic air gaps 258 c and258 d are different, respectively.

The magnetic air gaps 258 a and 258 d are arranged at positions offsetfrom each other by 180 degrees in electric angle and the magnetic airgaps 258 b and 258 c are arranged at positions offset from each other by180 degrees in electric angle. That is, the core 302 can be formed byrotating the core 301 by one pitch of magnetic poles. As a result, thecore 301 and the core 302 can be produced using the same mold so thattheir production cost can be decreased. The circumferential positions ofthe holes 310 of the cores 301 and 302 correspond to each other withoutany offset. As a result, the permanent magnet 254 fitted in each hole310 constitute an integrated magnet penetrating each of the cores 301and 302 without being divided in the axial direction. Of course, aplurality of divided magnets 254 may be arranged as being stacked in theaxial direction of the hole 310.

The rotating electric machine shown in FIG. 21(a) has a constructionsuch that a region 403 and a region 404 are arranged alternately. Theregion 403 in FIG. 21(a) is equivalent to the region 401 in FIG. 8(a)and the region 404 in FIG. 21(a) is equivalent to the region 402 in FIG.8(a). The rotating electric machine according to the present embodimentshown in FIG. 21(a) can be said to be electrically and magneticallyequivalent to the rotating electric machine according to the embodimentshown in FIG. 6(a) although positions at which the magnetic air gaps 258are different between the embodiments. That is, also in the presentembodiment, different torque fluctuations occur between the regions 403and 404 and they act so as to cancel each other, so that torquefluctuations can be reduced. Similarly to the first embodiment, themagnetic air gap 258 is formed at the assisted salient pole member 259,it gives substantially no influence on cogging torque. That is, byproviding the magnetic air gap 258, the influence of the cogging torqueto the fluctuation of torque can be suppressed and torque fluctuationswhen power is applied can be reduced substantially independently of thecogging torque.

As shown in FIGS. 21(a) and 21(b), the rotating electric machineaccording to the present embodiment includes the core 302 formed byrotating the core 301 by one pitch of magnetic pole and the axiallengths of the cores 301 and 302 are set to substantially the same asshown in FIG. 19(b), so that voltages generated in respective phasewindings of the stator coil 238 facing each pole can be madeapproximately equal to each other. As a result, substantially nocirculation current flows. However, substantially no circulation currentflows when the windings of respective phases of the stator coil 238facing the rotor 250 in the regions 403 and 404 are connected to eachother in series. Accordingly, it is no problem to use only the core 301or only the core 302.

Seventh Embodiment

FIGS. 22(a) and 22(b) show a rotor according to anther embodiment of thepresent invention. Other details than the above-mentioned are the sameas the above-mentioned embodiments.

FIG. 22(a) shows a rotor of the surface magnet type and FIG. 22(b) showsa rotor of the type in which a plurality of magnets is arranged in aV-shape. In either type of the rotor, the assisted salient pole member259 is between any two adjacent permanent magnets 254 and the magneticair gap 258 is arranged in the assisted salient pole member 259.Assuming that as seen from the inner periphery of the rotor 250, acentral axis between the permanent magnet 254 a and a next magnet on theleft side of the permanent magnet 254 a is named q-axis a and a centralaxis between the permanent magnet 254 b and a next magnet on the leftside of the permanent magnet 254 b is named q-axis b, the magnetic airgap 258 a is arranged offset to the right with respect to the q-axis aand the magnetic air gap 258 b is arranged offset to the left withrespect to the q-axis b. There is no magnetic air gap on both sides ofthe q-axis b. The magnetic air gap 258 a and the magnetic air gap 258 bare arranged symmetric with respect to a d-axis, which is a central axisof the magnetic pole. FIGS. 22(a) and 22(b) show A-A cross-sections ofthe rotor. Similarly to the above-mentioned embodiment, the B-Bcross-section has a shape formed by rotating the shape of the A-Across-section by one pitch of magnetic pole. As explained abovereferring to FIGS. 8(a), 8(b), and 8(c), the reduction of the torquefluctuations in the present embodiment is not affected by the magneticflux of the magnet, so that it does not depend on the shape of themagnet.

FIG. 23 illustrates achievement of reduction of torque fluctuations byproviding two magnetic air gaps 258 for each assisted salient polemember 259 according to the present embodiment. This shape is asfollows. Assuming that as seen from the inner periphery of the rotor250, a central axis between the permanent magnet 254 a and a next magneton the left side of the permanent magnet 254 a is named q-axis a and acentral axis between the permanent magnet 254 b and a next magnet on theleft side of the permanent magnet 254 b is named q-axis b, the magneticair gap 258 a on the right side with respect to the q-axis a is largerand the magnetic air gap 258 e on the left side with respect to theq-axis b is smaller. The magnetic air gap 258 b on the right side withrespect to the q-axis b is larger and the magnetic air gap 258 f on theleft side with respect to the q-axis b is smaller. The magnetic air gaps258 a and 258 b and the magnetic air gaps 258 e and 258 f are arrangedsymmetric with respect to a d-axis, which is a central axis of themagnetic pole. FIG. 23 shows an A-A cross-section of the rotor.Similarly to the above-mentioned embodiment, the B-B cross-section has ashape formed by rotating the shape of the A-A cross-section by one pitchof magnetic pole.

Eighth Embodiment

In the examples shown in FIGS. 20(a), 20(b), 22(a), 22(b), and 23, themagnetic air gap 258 is constituted by a groove provided in an outerperiphery of the rotor 250. However, the magnetic air gap 258 may beconstituted by a hole in the assisted salient pole member 259 as shownin FIG. 24(a). The magnetic air gap 257 and the magnetic air gap 258 maybe integrated as shown in FIG. 24(b). The magnetic air gap 258 may beachieved by providing the assisted salient pole member 259 with a regionthat has a different permeability than the rest as shown in FIG. 24(c).In FIG. 24(c), the permeability of the assisted salient pole member 259a is set to be lower than that of the assisted salient pole member 259b.

Ninth Embodiment

FIG. 25 illustrates the case where the stator coil 238 shown in FIG. 20is made of the concentrated winding type. The torque fluctuations in thepresent embodiment depends on the shape of the rotor 250 and hence thetorque fluctuations can be reduced in the case of the concentratedwinding type, which is a different winding method on the stator side,similarly to what is described above.

Various embodiments mentioned above have the following advantageouseffects.

-   (1) The magnetic air gaps 258 a and 258 b are provided in the    assisted salient pole member 259 and the magnetic air gaps 258 a and    258 b are arranged offset for each assisted salient pole member 259    so that the torque fluctuations when power is applied generated by    the magnetic air gaps 258 a and 258 b cancel each other. As a    result, the torque fluctuations of the rotating electric machine    when power is applied can be reduced. In particular, when the    rotating electric machine according to one of the embodiments that    can reduce the torque fluctuations when power is applied is employed    in a motor for driving a vehicle such as an electric vehicle or the    like, vibrations and noises when accelerating at low speeds can be    reduced, so that an electric vehicle that provides comfort ride    quality and is highly quiet can be provided.-   (2) When power is not applied, the magnetic air gap 258 gives    substantially no influence on the magnetic flux of the magnet.    Accordingly, a countermeasure to reduce cogging torque due to the    magnetic flux of the permanent magnet 254 and a countermeasure to    reduce torque fluctuations when power is applied can be separately    performed independently of each other. As a result, optimization of    magnet torque such that the cogging torque is small and the torque    when power is applied is large and a reduction in torque    fluctuations when power is applied can be concomitantly achieved.    Conventionally, a magnet is configured so that maximum torque can be    obtained and then skew or the like is applied so as to reduce    cogging torque. This has a defect that the torque (magnet torque)    becomes small. In the embodiments of the present invention, however,    the reduction in torque accompanying the reduction in torque    fluctuations can be avoided.-   (3) As mentioned above, the reduction in magnet torque accompanying    the reduction in torque fluctuations can be prevented, so that the    magnet can be made as small as possible and down-sizing and cost    reduction of the rotating electric machine can be achieved.-   (4) Since the torque fluctuations when power is applied is reduced    by offsetting the positions of the magnetic air gaps 258 a and 258 b    provided in the assisted salient pole member 259, it is unnecessary    to divide the permanent magnet 254 into a plurality of pieces in the    axial direction or skewing magnetization unlike conventional skewed    structures. The permanent magnet 254 includes a rare earth magnet,    typically a neodymium magnet. Rare earth magnets are shaped by    polishing, improvement of precision of production error directly    leads to an increase in cost. Therefore, the present embodiments in    which it is unnecessary to divide the magnet in the axial direction    allow cost reduction of the rotating electric machine. In addition,    there is no fear of an increase in fluctuation of performance or a    decrease in yield due to cumulative tolerances of magnets. As    mentioned above, according to the embodiments of the present    invention, an increase in productivity and a decrease in production    cost of the rotating electric machine can be achieved.

According to the above-mentioned embodiments, it is possible to achievea reduction in cogging torque and a reduction in torque fluctuationswhen power is applied. The reduction in torque fluctuations can beachieved by making the offset amount of the region of which themagnetoresistance has been varied differ for each magnetically-assistedsalient pole member such that the torque fluctuations when power isapplied due to the region of which the magnetoresistance has been variedcancel each other.

In the above-mentioned embodiments, the motor for driving a vehicle hasbeen explained as an example. However, the present invention is notlimited to motors for driving vehicles but also to various motors.Furthermore, the present invention is not limited to motors and can beapplied to various types of rotating electric machines, for example,generators such as alternators. So far as the features of the presentinvention is not damaged, the present invention is not limited to theabove-mentioned embodiments.

The disclosure of the following priority application is incorporatedherein by reference: Japanese Patent Application No. 2008-266952 (filedOct. 16, 2008).

EXPLANATION OF SYMBOLS

100 vehicle,

180 battery,

200, 202 rotating electric machine,

212, 214 housing,

230 stator,

232 stator core,

236 teeth,

238 stator coil,

250 rotor,

252 rotor core,

254 permanent magnet,

257, 258 magnetic air gap,

259 assisted salient pole member,

301, 302 core,

310 hole

1. A rotor comprising: a plurality of magnets; a rotor core comprising aplurality of holes in which the magnets are provided; wherein theplurality of magnets are arranged in regions of alternating polarity,wherein each of said regions has at least one magnet; a plurality ofmagnetically-assisted salient pole members, each of which is provided ina core portion between the regions; a first magnetic air gap formed withan edge of each of the magnets and the holes; and a second magnetic airgap provided in each of the magnetically-assisted salient pole membersalong an axial direction of a rotation axis at a position offset in acircumferential direction of the rotation axis from a q-axis passingthrough a salient pole center of each of the magnetically-assistedsalient pole members, wherein the second magnetic air gap is formedindependently from the first magnetic air gap; and the second magneticair gap is provided on every other pole of the magnetically-assistedsalient pole members, and a pole provided with the second magnetic airgap and a pole without the second magnetic air gap are alternatelyarranged.
 2. The rotor according to claim 1, wherein a magnet hole poleradian τg/τp is set from 0.5 to 0.9, wherein τp indicates pole pitch ofthe permanent magnet and τg indicates an angle for the magnet and thefirst magnetic air gap on both sides thereof.
 3. The rotor according toclaim 2, wherein the magnet hole pole radian τg/τp is set from 0.7 to0.8.
 4. The rotor according to claim 1, wherein the second magnetic airgap is a groove provided on an outer periphery of the rotor core.
 5. Arotating electrical machine comprising: a stator having a stator coil;and a rotor provided rotatably around a specific rotation axis withrespect to the stator, wherein the rotor includes: a plurality ofmagnets; a rotor core comprising a plurality of holes in which themagnets are provided; wherein the plurality of magnets are arranged inregions of alternating polarity, wherein each of said regions has atleast one magnet; a plurality of magnetically-assisted salient polemembers, each of which is provided in a core portion between theregions; a first magnetic air gap formed with an edge of each of themagnets and the holes; and a second magnetic air gap provided in each ofthe magnetically-assisted salient pole members along an axial directionof the rotation axis at a position offset in a circumferential directionof the rotation axis from a q-axis passing through a salient pole centerof each of the magnetically-assisted salient pole members, wherein thesecond magnetic air gap is formed independently from the first magneticair gap; and the second magnetic air gap is provided on every other poleof the magnetically-assisted salient pole members, and a pole providedwith the second magnetic air gap and a pole without the second magneticair gap are alternately arranged.
 6. The rotating electrical machine toclaim 5, wherein a magnet hole pole radian τg/τp is set from 0.5 to 0.9,wherein τp indicates pole pitch of the permanent magnet and τg indicatesan angle for the magnet and the first magnetic air gap on both sidesthereof.
 7. The rotating electrical machine to claim 6, wherein themagnet hole pole radian τg/τp is set from 0.7 to 0.8.
 8. The rotatingelectrical machine to claim 5, wherein the second magnetic air gap is agroove provided on an outer periphery of the rotor core.